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Frequently Asked Questions

Water Wise Gardening

1. What difference can water wise gardening make?

The highveld area was originally grassland with the more wooded areas towards the Magaliesburg and into some of the mountain ranges. This landscape could survive on rainfall alone.

  • Through urbanisation, Gauteng has become the world’s largest urban forest, with over 10 million trees in gardens, parks, golf courses, sports grounds and streets. The urban landscape has changed from one that could survive on rainfall alone, to one that requires regular, year-round watering.
  • Water used in landscapes accounts for an estimated 31% to 50 % of water supplied for domestic/urban use.
  • The more landscapes that are designed & planted, the more water is used by our society. Urbanisation is increasing at an astonishing rate, which calls for more new landscapes to be created, and therefore puts even greater pressure on SA’s available water resources.
  • Applying Water Wise principles in a garden or landscape can save 10% to 32% of water used

2. How Do Invasive Alien Plants Affect Water Supply?

Invasive alien plants waste 7% of our water resources – Tree invaders of river courses and catchments drastically reduce the volume of water that reaches rivers and dams, and can even cause streams to stop flowing or wetlands to dry up.

What is an invasive alien plant (invader for short)?

  • Non-indigenous plants that take over areas of indigenous vegetation.
  • Indigenous plants can become invaders in areas that they are not endemic to.

What makes an alien plant become an invader?

  • Absence of natural enemies.
  • Similar conditions to native country - 45% of the 30 plants introduced from Australia have become problem plants.
  • Vegetative reproduction.
  • Prolific seed production, long-lived seeds.
  • Effective seed dispersal mechanisms, such as water, wind and birds.

Key statistics:

  • 750 tree species and 8 000 herbaceous species introduced into South Africa.
  • 1 000 naturalised, 200 invasive.
  • Over 10 million hectares of land have been invaded.

What happens if we do nothing?

  • If nothing is done, the problem will double within 15 years.
  • Estimated cost of controlling invaders - R600 million a year over 20 years.
  • Plant invaders can cause mass extinctions of indigenous plants and animals. Several fynbos species are already extinct, and many others are facing extinction.
  • Invaders impact farming by encroaching on arable land or grazing, poisoning stock animals and getting tangled in wool. Their control inflates the production costs drastically, and in low production areas such as the Northern Cape, the control of invaders often costs more than the land itself.
  • Invaders also intensify flooding and fires; cause erosion, destruction of rivers, siltation of dams and estuaries, and poor water quality.
  • Aquatic weeds form dense mats that block pump inlets, restrict the use of boats, reduce flow in canals, cause siltation of rivers and increase water loss by evapotranspiration. They provide breeding sites for mosquitoes and bilharzia snails, and by blocking sunlight, affect the entire food chain which reduces aquatic biodiversity.

What can I do to help?

  • If you own land, keep it clear of invading alien plants.
  • Do not buy invasive alien plants from nurseries.
  • Buy firewood, charcoal, crafts, furniture, toys, building material, mulch, etc made from invaders.
  • Do not bring foreign plants and animals into our country – and do not send ours to other countries.

Where can I find more information?

Source: Rand Water, Water wise Gardening booklet

3. General principles of water wise gardening.

Primarily it's about the wise use of our water resources.

We need to adapt our gardening lifestyles and habits to make the most of our scarce water resources, as in the long run it is our gardens and us the gardeners who will suffer when there isn’t enough water to cater for this lifestyle and for these demands.

  • It includes:
    • Garden design - Zoning your garden into high, medium and low water use areas, which can include container planting
    • Re-using runoff rainwater
  • Mulching
    • Placing the right plants in the right zone
    • Replacing invasive alien plants with indigenous alternatives
    • Minimising lawn area, or training the lawn to need less water
    • Making irrigation systems water efficient
  • Watering schedule – Applying the correct amounts of water, at the right time, not over-watering and turning off water when it is not needed
  • Choosing water features that don’t waste water. Improving the soil by composting to increase soil water-holding capacity
  • Choosing plants that are Water Wise and low maintenance

Garden design

  • Ideally, your garden is designed on Water Wise principles from the start. For an established garden – plan new beds on Water Wise principles, replace plants in the low/ medium zone with Water Wise varieties, and reconsider next season’s planting of annuals.
  • Zoning into high/ medium/ low water use areas
    • Don’t create long winding borders of colour throughout the garden using thirsty annuals. As much as what it may look good, it is impractical to water this type of garden correctly. Rather group the annuals to create focal points at entrances or entertainments areas, and water this area separately as a high zone. Another option is to use colourful plants with low or medium water needs to create borders (see Plant choice), as the whole bed is then a low or medium zone and can be watered correctly.
    • Containers are an ideal way of creating colour and interesting features in the garden, while keeping high water use plants in a designated (container) zone.
  • Plant in spring or autumn, when the water requirements are lower.

Re-using runoff water

  • Catch rain-water in a rainbarrel for use on dry days – ideally this should be elevated so the water can be gravity-fed to the rest of the garden, and the tap should be about 20cm above the bottom to avoid picking up the junk that collects in the bottom and blocking the hose and fittings.
  • Direct downspouts to deliver water to flower beds – if the force of the water is too strong, use mulch (e.g. pebbles) to break the force and spread the water out.
  • Berms and swales can be used to direct runoff water, e.g. swales on a driveway, channels lined with plastic and filled with pebbles.


  • Mulching can reduce evaporation by up to 70%.
  • Mulch also suppresses weed growth.
  • Mulch is most effective for young plants, which are the most susceptible to water shortages because they are too small to have any water reserves, and their root systems are too shallow to reach water deeper in the soil profile. One word of caution - leave space around the stems of young plants, to avoid rot.
  • There are different types of mulch:
    • Compost
    • Bark chips
    • Wood chips (there are even coloured varieties available)
    • Nut shells
    • Pebbles
    • Pine needles (these may affect pH, so rather use around acid-loving plants)
    • Strips of paper
    • Straw
    • Plastic sheets (particularly useful for areas like paths where you want a decorative mulch without having to worry about weeds)
    • Hessian
    • Even grass clippings (ensure these are completely dry, and only scatter a thin layer)
    • Living mulches, e.g. groundcovers.
  • Dig a basin around the base of plants to hold water long enough for it to sink in. Filling the basin with mulch will reduce evaporation.
  • Improving the soil
  • Rather use compost than fertiliser – it provides nutrients, while at the same time improves the water-holding capacity of the soil.
  • Plant choice
  • When we look at books or visit the coast or Mpumalanga we get all enthused about certain designs, plants and ideas but often fail to take note of the water requirements of that idea or plant.
  • Alien invader plants should be taken out – these use more water than the indigenous plants that would grow in the same area.
  • Select plants that are hardy and don’t require much watering:
    • Grey foliage
    • Waxy cuticle
    • Hairy leaves
    • Aromatic oils
    • Reduced leaf area.
  • Not all annuals use a lot of water and can be surprisingly tolerant of little water.
    • Gazania
    • African Daisy
    • Coreopsis
    • Cosmos
    • Californian poppy
    • Marigold
    • Verbena
    • Kochia
    • Drosanthemum (succulent)
    • Nierembergia and
    • Penstemon to name a few.


  • Keep lawn areas to a minimum, as these use a lot of water.
  • High traffic areas can be paved or mulched, and areas of lawn that are not used should rather be made into beds.
  • Lawn can be “taught” to get by on less water – see “How much to water”.
  • Try not to cut lawns too short. When mowing, cut only the top third of the leaf area, leaving it 3cm or longer.
  • When to water
  • Watering in the early morning or late afternoon reduces water lost to evaporation – if you have a timer on your irrigation system, these are the ideal times.
  • Certain fungal diseases break out when the leaves have been wet for a certain period – e.g. water late afternoon, leaves are wet all night, then water again in the morning – wait for the leaves to dry out before watering again.

How much to water

  • On the Highveld, the evaporation is 4 to 6mm per day in summer depending on the angle and location of the property. In winter this goes down to almost 0mm. When watering, you need to replace the water that has evaporated, as well as give the plants the water they need. If a plant requires 10mm of water every 3 days, you therefore need to put down 10mm plus the 15mm or so that has evaporated over those 3 days, a total of 25mm. Mulching the soil can dramatically reduce water loss due to evaporation, meaning that you can water less often. To calculate how much water you are putting down, place a measuring jug under your sprinkler or irrigation system. Time how long it takes for the jug to fill up to 25mm, and then you will know how long to let your sprinkler run for.
  • Water only as rapidly as the soil can absorb the water, as runoff water is wasted. Shallow basins around the base of trees and shrubs can hold water, giving it time to sink into the soil.
  • Water according to season. There is much less evaporation in the winter, and many plants are dormant, so you need to water much less than in summer.
  • Water your plants deeply but less frequently to encourage deep root growth that will sustain the plant during dry periods. Frequent watering causes the plant to develop roots in the first few centimetres of soil only, so in dry periods they cannot use water deeper down in the soil profile. This is particularly true of lawns. It is possible to ‘train’ your plants to need less water, by gradually changing from frequent shallow watering to less frequent but deeper watering schedule.

Irrigation systems

  • Don’t irrigate if it has just rained – use the 4 day weather forecast to plan whether you should irrigate or wait for the rain. Some irrigation systems have rain sensors, which automatically turn the system off if there has been rain.
  • Water according to season.
  • Install a timer to avoid over-watering. Once you have calculated how much water the system puts down in a given time period, you can adjust the timing so that the plants get what they need, without over-watering.
  • Drip irrigation systems are the most Water Wise, as these supply water directly to the roots and there is no water loss due to evaporation or droplets being blown away. It is important to maintain these systems carefully, e.g. if a joint comes apart, to flush the system of any dirt that may have got in.
  • For other irrigation systems, it is more Water Wise to have a system that delivers big drops of water close to the ground – fine droplets of water are easily blown away, and may only wet the foliage where heavier droplets will fall to the soil.
  • An important Water Wise principle is zoning, where the garden is divided into high and low water use zones. In order to water these zones accordingly, you will need to have separate irrigation circuits for each one.

Water gardens

  • Ponds or bog gardens can be WaterWise
  • Consider where this garden is placed carefully – ideally it should be at the lowest point in the garden, to collect surface runoff water.
  • Direct downspouts to this area.
  • Design it along ecological principles, and it will need little maintenance.
  • Water features
  • Fountains that spray water up into the air are the least Water Wise, as droplets are easily blown away.
  • Trickle or cascade water features are the most Water Wise.
  • Consider placement too – more water will evaporate from a feature that is in full sun vs. one that is in a shady area.


  • Use a broom to sweep driveways, not the hose.
  • Weed regularly – weeds compete with plants for nutrients and water.
  • Use a pool cover when it is not in use.
  • Check for leaks in pipes, taps, irrigation systems.
  • While fertilisers promote plant growth, they also increase water consumption. Apply the minimum amount of fertiliser needed – alternatively, use compost.

For further information or enquiries please contact us on:

Tel: 0860 10 10 60
Fax: 0860 10 10 60

Source: Rand Water, Water wise Gardening booklet